How to access body from POST request (using 'fetch()') inside my Extbase Controller

I’m sending a POST request via fetch() from my JavaScript Service-Worker to my TYPO3 Extbase controller action.
The controller then goes on to process the data, but I can’t find a way to get the body data.

I’m calling the Action through an Extbase RouteEnhancer, but I think this shouldn’t affect my Problem.

in the Service Worker: javascript

fetch("myDomain.de/my/route/Enhancer/", {
  method: "POST",
  headers: {
    "Content-Type": "application/json"
  },
  body: JSON.stringify({ cookieValue: cookie})
})

in the Controller extbase php

    public function syncAction()
    {
        ?? Get Body from fetch() here??
        return file_get_contents('php://input'); <-- is empty
    }

I want to retrieve the body data from fetch.

I’ve tried:

$request = $GLOBALS['TYPO3_REQUEST'];
$data = $request->getParsedBody();

returns NULL

$data = $this->request->getParsedBody();

returns NULL

file_get_contents('php://input'); 

is empty

Am I missing something?
Is this the right way to approach or may there be a better solution to send the data?

>Solution :

Since TYPO3v11 you can access $this->request for the (decorated) request. This way you can access the request body:

$this->request->getBody()

However, since this will only give you the body as raw stream, you can use this convenience wrapper:

$this->request->getParsedBody()